9712 Nauplius /ˈnɔːpliəs/ is a mid-sized Jupiter trojan from the Greek camp, approximately 33 kilometers (21 miles) in diameter. It was discovered during the second Palomar–Leiden Trojan survey at the Palomar Observatory in 1973 and later named after Nauplius the Wrecker, from Greek mythology.^[1] The dark Jovian asteroid has a rotation period of 19.4 hours.^[8]

Nauplius was discovered on 19 September 1973, by Dutch astronomer couple Ingrid and Cornelis van Houten at Leiden, on photographic plates taken by astronomer Tom Gehrels at the Palomar Observatory in California.^[1] The body's observation arc begins with its official discovery observation at Palomar.^[1]

Nauplius is a dark Jupiter trojan in a 1:1 orbital resonance with Jupiter. It is located in the leading Greek camp at the Gas Giant's L₄ Lagrangian point, 60° ahead on its orbit (see Trojans in astronomy).^[4] It is also a non-family asteroid of the Jovian background population.^[5] It orbits the Sun at a distance of 4.6–5.9 AU once every 12 years (4,374 days; semi-major axis of 5.23 AU). Its orbit has an eccentricity of 0.13 and an inclination of 8° with respect to the ecliptic.^[3]

This minor planet was named after Nauplius, a son of Poseidon and Amymone. He was a king of Euboea and the father of Palamedes, who was killed after a false accusation by Odysseus during the Trojan War. Nauplius revenged the death of his son by placing lights on the cliffs of his kingdom, causing the Greek fleet to shipwreck on its return from Troy.^[1] The official naming citation was published by the Minor Planet Center on 2 April 1999 (M.P.C. 34355).^[10]

Nauplius is an assumed C-type asteroid, while the majority of larger Jupiter trojans are D-types.^[8]